Exemplary embodiments of the present invention relate to laser weapon system. In particular, exemplary embodiments of the present invention relate to a beam focusing unit for a laser weapon system having high movement dynamics and high output power at the same time. Furthermore, exemplary embodiments of the present invention relate to a structure of a beam focusing unit of a laser weapon system on the basis of diode-pumped lasers operated with electrical energy.
Laser weapon systems including laser sources and associated optics that enable to deploy laser weapon systems against different classes of targets are known. Possible deployment scenarios are, for example, self-protection of platforms or offensive deployment. Common to both deployment scenarios is the use of high energy lasers.
Such laser weapon systems can be used against static targets such as, for example, mines, barricades or improvised explosive devices (IED), and also against dynamic targets, specifically as part of the defense against threats by flying objects such as rockets, artillery and mortar (RAM), against guided missiles with and without seeker heads, or against drones or unmanned aerial vehicles (UAV).
For combating such targets, conventional optical radiated power outputs are used that reach well into the range above 100 kW of optical output power.
Naturally, a potential threat normally occurs without advance warning and from an unknown direction, and effective combating the threat requires suitable focusing of a laser weapon system within a few seconds up to fractions of a second.
Operational laser weapon systems therefore require a configuration that enables combating targets and thus enables focusing an active beam, hence the laser radiation emitted by the system, within an entire half-space (i.e., hemisphere) around the laser weapon system. It is important here that focusing and a possible subsequent tracking of a target may require both high spatial movement dynamics as well as precision.
Combating targets in overflight scenarios (the threat flies over the laser weapon system) places special demands on a laser weapon system since in the region of the zenith problems in the form of extremely high focusing speeds and accelerations can occur, which are relevant when tilting over, thus a complete half-space movement, of the beam focusing system is not possible.
A laser weapon system can possibly be implemented using a fiber laser as a laser beam source. Here, transmitting the optical radiated power between laser beam source and beam transmitter is carried out via trailing fiber optics. However, with the optical radiated power outputs and beam qualities that occur, fiber optics are possibly limited in terms of length and also in terms of implementable bending radii since in the case of great lengths, non-linear effects such as, for example, stimulated Raman scattering or thermal effects can occur, which can limit the transmittable power output. Increasing the fiber diameter, in turn, can result in deterioration of the beam quality.
Suitability of a laser source for a laser weapon system is in most cases determined by the mode quality or beam divergence, the spectral properties and the optical power output of the laser source. For implementing a laser weapon system of, for example, 10 kW optical power, the freely available fiber length is normally kept below 2.5 m. However, such a short length normally does not allow implementing a laser weapon system that functions according to the concept of trailing fiber optics and, at the same time, implements movability over large portions of the spatial angle, in particular of a half-space.
A laser weapon system, independent of the type of the embodiment of the actual laser-active medium, for example as a rod, slap, fiber or disc laser, typically comprises a diode-pumped solid state laser. However, a laser weapon system can also be implemented by using liquid, gas or metal vapor lasers, which requires converting the primary energy, e.g., in the form of electrical energy, into radiation energy for optically stimulating the laser-active medium uses a significant number of semiconductor lasers or diode lasers.
In addition to beam generation, a laser weapon system needs a multiplicity of functional elements such as power supply, buffering, cooling, mechanical structure, optical elements, sensors and actuators.
A generic architecture of the functional components of a laser weapon system is illustrated in FIG. 1.
Here, an energy supply and processing unit acts on the pumping sources which, by using the laser medium, generates an active beam that is subsequently introduced in the beam control unit. The beam control unit consists of a beam coupling with subsequent beam conditioning, and of elements for enabling focusing the beam, for example, on a target. The active beam subsequently propagates via possible optical elements in the beam path and normally through the earth's atmosphere toward the target, which can be marked by a target illuminator. On the target, the beam induces an effect. Sensors and control electronics can detect, e.g., turbulences of the atmosphere and also target movements, and by using a suitable controller, can reposition or refocus the active beam.
Such a multiplicity of functional elements and auxiliary devices for operating the same add up to a significant weight. For example, a laser weapon system in the power range of 100 kW typically weighs several tons. In this respect, a reduction of the power-to-weight ratio of below 50 kg per kW is unlikely even in the future.
In the case of high-energy laser weapon systems, the obvious possibility of avoiding trailing fiber optics, namely the implementation of a structure with the laser beam source and beam transmitter being rigidly coupled as a whole cannot be employed due to the resulting significant mass to be moved and the focusing dynamics and accuracy that are finally to be implemented because of this.
A possible alternative implementation of a laser weapon system is based on the concept of separating the laser weapon system into a static part (beam generation including auxiliary aggregates and platform), and a movable part (in particular the beam transmitter) that follows the target. In the static part, preferably, all elements comprising a mass or a volume are to be arranged so as to keep the movable part, which has to follow the target, as light and agile as possible.
FIG. 2 shows such a division of the functional components into a detached part, a stationary part, and two drive parts that are substantially separated from each other. The detached part can consist of a generator for generating the required energy, and of the functional elements thereof such as cooler and cooling water supply. The generated energy is fed via a supply unit to the stationary part in which the laser generating unit is arranged. Subsequently, the generated active beam is focused in a two-part movable part on a target, for example. The movable part can be divided into a rough drive which, in first instance, can be rotated about an axis, for example the azimuth axis, and into a second part having a second axis, for example the elevation axis.
However, in a system according to FIG. 2 the active beam generated by the laser beam source(s) may have to be guided to the beam transmitter, which can be configured as a telescope, by two axes that are movable within a wide angular range. A possible way of decoupling rotational movements between different parts of a beam focusing system that move relative to one another, and of transmitting the optical radiated power from one part to the next one would principally be monolithic rotary transmitters/couplings for fiber optics. However, they cannot be implemented in the radiated power and beam quality categories that are of interest for a laser weapon system. This particularly applies if, to increase the power output through beam coupling, a plurality of independent beams are to be transmitted to a beam coupling unit flanged onto the beam transmitter.
A possible implementation of a suitable transmission is a free-beam transmission between laser beam source and beam transmitter, which are normally implemented such that movement axes or rotational axes of a beam focusing system coincide at least in sections with the longitudinal extension direction of a partial free-beam transmission. For this, known astronomical telescopes are available, wherein the beam guidance is implemented in the reverse direction (i.e., from the outside through the telescope to a sensor or measuring instrument). Such a principle is known as coudé focus or (for an axis) as Nasmyth focus.
However, since in astronomical telescopes the boundary conditions of transmittable light outputs (in the nanowatt range) in comparison to several 100 kW for laser weapon systems, and also the required focusing speed and necessary kinematic dynamics are significantly different, which, at the same time, entails a considerable impact on the design of the optical elements, on the mechanical construction and on the necessary focusing drive including sensors and control, astronomical telescopes do not represent a suitable platform for the development of a laser weapon system.
Exemplary embodiments of the present invention relate to a laser weapon system having a novel connection of laser generating element and beam optics element in such a manner that high spatial dynamics and precision of focusing of an active beam can be implemented without having to accept a deterioration of the properties of the active beam during the transmission to the beam optics element.
In particular, focusing speeds of >=1 rad/s, focusing accelerations of >=1 rad/s2 and a focusing accuracy of >=5 μrad are implementable within the scope of the present invention.
In accordance with exemplary embodiments of the present invention the beam transmission is configured to a beam focusing system of a laser weapon system in such a manner that an output element unit situated at the end of the amplification chain of a laser source and finally determines the mode quality or beam divergence, spectral properties and, in particular, the optical power of the radiation emitted by the laser source, is separated or detached from the remaining laser generating components and is arranged on the fully movable part of the focusing system, which movable part belongs to the focusing unit or beam optics element of the laser weapon system.
Here, the structure is configured such that a system is created in which the active beam finally focused on a target can be focused in the full half-space surrounding the laser weapon system, wherein the power transmission between the elements, in which the energy conversion from an energy form into optical radiation energy takes place, and the final optomechanical element responsible for focusing the beam on the target is carried out in such a manner that the power transmission to an output element unit is carried out via a fiber-optic connection or fiber-optic elements and is arranged on that part of the laser weapon system that is set up for targeting and/or target-following. Here, transmitting the optical energy is in particular carried out via at least one movable axis and not via free-beam guidance.
In accordance with exemplary embodiments of the present invention the beam source is functionally divided in such a manner that, in consideration of volume and mass, separation of the components of the beam sources is carried such that they are separated into such components which, on the one hand, decisively determine the mode quality or beam divergence and the spectral properties and, on the other, the optical power.
In particular, an output element unit that decisively determines the output beam quality but is responsible only for a fraction of the total volume and the total mass of a radiation source is directly coupled to the movable part of the beam focusing unit and moves with the same during each focusing process, while the output element unit is supplied via fiber-optic elements with optical radiated power which is generated in the pumping sources which, together with the associated auxiliary aggregates such as energy supply, cooler etc., are decisive for the majority of the total volume and the total mass of a beam source, wherein the pumping sources are arranged in a stationary or at most partly movable part of the system. Transmitting the power and the optical signals between the two parts of the stationary/partly movable part and the fully movable part takes place via fiber-optic elements which, however, do not need to have the same optical quality or power capacity as, for example, the connection of output element unit and beam optics element.
This arrangement achieves the advantages of a fiber-optic power transmission over a free-beam transmission such as, for example, robustness, independence from adjustments, insensitivity to harmful environmental influences, flexible geometrical configuration and low volume and mass can be maintained without significantly limiting the available focusing region (hemisphere), without unnecessarily increasing the total volumes and masses to be moved on a movable part of a beam focusing system beyond the necessary level, and without the need of significantly cutting back in terms of mode quality or beam divergence, spectral properties and optical power, and therefore (spectral) irradiance available on a target. The operational reliability is also increased at the same time.
It should be understood that the fully movable part of the laser weapon system is the part that is set up in a freely movable manner in the half-space for targeting and/or target-following. A partly movable part or stationary part can be arranged, for example, on a transport platform so as to keep the entire laser weapon system transportable between different operational areas or operational sites, without this movement influencing the actual operation of the laser weapon system in terms of targeting and target-following.
An output element unit according to the invention can be configured as a fiber laser, wherein the output element unit can be implemented with a fiber output again, but with a significantly shorter length than would be needed if the output element unit would not be arranged on the fully movable part, a so-called fully movable fiber length, or can already be implemented as a free beam. In both cases, the fiber-guided path of the signal transmission ends only in the fully movable part of the focusing unit belonging to the laser weapon system. A fiber-based connection to the output element unit is therefore still necessary; however, since the functional configuration of the output is set up on the fully movable part of the laser weapon system, this fiber transmission can be configured differently, it is in particular not necessary to transmit the traditionally needed high power outputs and/or high beam quality without losses.
Also, the output element unit can be configured as an optically pumped laser source, wherein the medium is configured as a rod, slap or disc laser, or is configured as a number or combination of such geometries. The connection of the output element unit to a beam focusing unit can be configured as an optical fiber or as a free beam. An output element unit according to the invention does not necessarily have to provide an increase of the optical output power of a laser source, thus a power amplification of considerably greater than 1. Rather, an output element unit according to the invention can be configured in a largely passive manner, thus non-amplifying, and can in particular compensate deteriorations of beam properties with regard to mode quality or beam divergence, or spectral or time-depenent properties of the beam, which deteriorations occur during the transmission of upstream output units, and/or can improve the output beam.
Here, the concept according to the invention is not limited to the use of a single beam source; rather, it can also be applied to the principle of beam coupling a plurality of laser sources. In such a case, a plurality of output element units of the respective individual laser beam sources can be used, which output element units connect in an equivalent manner to a subsequent beam coupler that is also located on the fully movable part of the beam focusing system.
According to the invention, this results therefore in a laser weapon system that can be focused in the full half-space, and which avoids the properties of the active beam being negatively influenced through a fiber length necessary for beam transmission of the output power of the laser system by using trailing fiber optics. Also, avoided is the use of a free beam of high power via rotational axes, the guidance of which free beam puts high accuracy demands on the components used and on the one or a plurality of axes that are moved relative to one another and to a stationary reference system, and it is avoided at the same time that the laser sources of the laser system required for generating the laser beam, or at least particularly voluminous or high-mass parts thereof such as pumping sources, energy supply, storage and cooling system do not have to be moved together with the fully movable part of the beam focusing unit during a focusing process.
Furthermore, the solution according to the invention results in increased reliability and operational readiness of an overall laser weapon system since, due to the structure according to the invention, the number of elements involved in the beam guidance is significantly reduced and can be limited substantially to monolithic fiber elements, in particular in the movable part. Also, for example in the case of beam coupling, it arises that a failure of an individual string can no longer have a catastrophic effect on the function of the overall system.
Further exemplary embodiments and advantages of the present invention arise from the following description of the figures. In different figures, identical or similar elements are designated by identical or similar reference numbers.
The illustration in the figures is schematic and not to scale; however, it may represent qualitative proportions.